JP3893339B2 - Optical communication module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical communication module capable of bidirectionally transmitting and receiving optical signals, and more specifically, using a plastic optical fiber as a transmission medium for home communication, communication between electronic devices, LAN (Local Area Network), and the like. It is related with the optical communication module which can be used.
[0002]
Communication using an optical fiber as a transmission medium has been attracting attention since long-distance transmission and high-speed transmission are possible. As an optical fiber, a single mode fiber or a multimode fiber using a glass as a base material is mainly used. Glass optical fiber (GOF) is used for long-distance / high-speed communication because of its low transmission loss and large transmission band. However, these optical fibers have a very small core diameter of 5 to 80 μm, and it is necessary to control the alignment and the coupling with the optical communication module with high accuracy. Therefore, expensive optical fiber plugs and optical systems are required. Become.
[0003]
In recent years, with the reduction in loss and bandwidth of plastic optical fibers (POF), mounting of optical communication modules using POF as a transmission medium for in-home communication and communication between electronic devices is being studied. Compared to GOF, POF is still unsuitable for long-distance and high-speed transmission, but it has a large aperture of about 1 mm, so it can be easily combined with optical communication modules compared to GOF. Therefore, there is an advantage that an inexpensive and easy-to-use optical communication link can be obtained.
[0004]
The characteristics of GOF and POF differ greatly, and optical communication modules that take advantage of each advantage have been developed. GOF has an advantage that long-distance and high-speed transmission is possible, but an alignment technology with high accuracy is required, and the optical communication module becomes expensive. FIG. 4 shows an example of an optical communication module using GOF. The optical fiber 102 is attached to the plug 107 after being bonded to the ferrule 121 and having its end face processed. The optical communication module 101 includes a receptacle 110 having an opening for inserting a plug 107, a transmission lens 106, and a light emitting element 104. As described in JISC-5970 and the like, each component has an accuracy of the order of several μm. In addition, it is necessary to assemble each component with high accuracy, and the optical communication module 101 is relatively expensive.
[0005]
An example of an optical communication module using POF is shown in FIG. Since POF has a large core diameter and does not require alignment with high accuracy, an expensive ferrule is not required and only a simple plug 107 can be used. Examples of the plug 107 include an optical mini jack (OMJ) used for transmitting an audio digital signal. The optical communication module 101 is composed of a light emitting element 104 formed integrally with a molded lens 106 and a receptacle 110. Since the POF has a large diameter, the shape accuracy thereof may be as large as several tens to 100 μm and is inexpensive. Thus, the optical communication module 101 that can be easily assembled is obtained. For example, the accuracy of the core diameter of POF itself is defined as ± 60 μm in JISC-6837. 4 and 5 both show a case of a transmission module used for one-way communication.
[0006]
On the other hand, in the optical communication module using an optical fiber as a transmission medium, both the transmission and reception of signal light in the full-duplex mode at the same wavelength, as shown in FIGS. There is an optical communication module that performs. Conventionally, this type of optical communication module has mainly used two optical fibers. However, when two optical fibers are used, there are problems that it is difficult to reduce the size of the optical communication module and that the cost of the optical fiber increases as the transmission distance becomes longer. For this reason, an optical communication module that performs full-duplex optical communication using one optical fiber has been proposed.
[0007]
In such an optical communication module, since transmission and reception are performed by the same optical fiber, it is important to prevent interference between transmission light and reception light. The main causes of interference of the transmitted light with the received light are when the transmitted light is reflected at the end face of the optical fiber when entering the optical fiber (hereinafter referred to as “near end reflection”), and inside the optical communication module. Some of these are scattered light (hereinafter referred to as “inner light”).
[0008]
In an optical communication link using an optical fiber as a transmission medium, it is important to couple the received light emitted from the optical fiber to the light receiving element with high efficiency in order to obtain a high signal to noise ratio (SN). .
[0009]
As a conventionally proposed optical communication module for single-core full-duplex communication, there is a method of separating transmitted and received light using a polarization separation element. That is, while the received light that has propagated through the optical fiber has a random polarization direction in the middle of propagation, the reflected light (near-end reflection) reflected from the end face of the optical fiber has the same polarization direction. Therefore, interference due to near-end reflection can be prevented by disposing a polarization separation element that reflects only light having this polarization between the optical fiber and the light receiving element. However, in this method, since about half of the received light is reflected by the polarization separation element, a reception loss of about 3 dB occurs, and the light cannot be efficiently used. There was a problem that (LED) could not be used.
[0010]
For this reason, Japanese Patent Application Laid-Open No. 11-27217 and the like disclose a method in which transmission light is incident on a position shifted from the center of the optical fiber and received light emitted from other regions of the optical fiber is received. This method will be described with reference to FIG. The transmission light 108 emitted from the light emitting element 104 is collected by the transmission lens 106, reflected by the rising mirror 115, and incident on a position shifted from the optical axis center of the end face of the optical fiber 102. Received light 109 emitted from the optical fiber 102 is coupled to the light receiving element 105. The end surface of the optical fiber 102 is processed into a curved surface or an inclined surface, and the reflected light 114 reflected by the end surface of the optical fiber 102 is reflected in the outer peripheral direction of the optical fiber 102 to prevent interference due to near-end reflection.
[0011]
FIG. 7 shows the relationship between the coupling position of the transmission light 108 on the end face of the optical fiber 102 and the reception area. In the system in which the transmission light 108 is incident on a position shifted from the center of the optical fiber 102, the end surface of the single-core optical fiber 102 is spatially divided into a transmission area where the transmission light 108 enters and a reception area as shown in FIG. To achieve single-core full-duplex communication. In this method, by making the reception area larger than the transmission region, it is possible to separate transmitted and received light with a loss less than the loss of about 3 dB in the method using the polarization separation element. That is, in such a system, the reception efficiency can be improved by making the reception area larger (that is, making the transmission area smaller and making it enter the outer peripheral portion of the optical fiber 102). Since the core diameter is small in GOF, it is difficult to adopt this spatial separation method. However, in POF, it is easy to spatially separate transmitted light and received light using the large-diameter core. It is. Further, since it is not necessary to assemble with higher accuracy than the GOF, and the optical system can be configured with relatively simple and inexpensive optical components, the optical communication module 102 for single-core full-duplex communication is inexpensive. Can be obtained.
[0012]
Further, POF has a feature that its end face can be easily processed. In the end face processing with GOF, it is necessary to bond a cut fiber strand to a ferrule processed with high precision dimensional accuracy, and then perform mirror finishing with an expensive polishing apparatus. On the other hand, POF has a large core diameter and does not need to be managed with high precision, so no ferrule is required. The wire is directly bonded to the plug, and the end face is simply pressed against a hot plate of any shape and melted. Can be processed. The end face shape of the optical fiber may be processed into an inclined surface or a spherical surface in addition to a plane perpendicular to the optical axis. In GOF, the transmitted light emitted from the light emitting element is often reflected by the end face of the optical fiber and is coupled to the light emitting element again, so that an inclined surface is often used to prevent the oscillation state from becoming unstable. On the other hand, with POF, the accuracy of the optical system is low, and the transmitted light reflected by the end face of the optical fiber is difficult to return to the light emitting element, and the communication speed is relatively slow. However, as described above, when performing single-core full-duplex communication, in order to prevent the reflected light 114 of the transmission light 108 from being coupled to the light receiving element 105 and causing interference due to near-end reflection, a spherical surface or an inclined surface is used. There is a case.
[0013]
FIG. 8 shows an example of a plug shape for a conventional plastic optical fiber, where 102 indicates an optical fiber and 107 indicates a plug (OMJ) 107. POF can be processed into an arbitrary shape by melting its end face with a hot plate. FIG. 8 shows a case where the end surface is a spherical surface. When the end surface is melted in this way, the tip of the plug 7 has a tapered portion 12 whose inner diameter increases as it goes to the tip as shown in FIG. By having the plug inclined portion 12, the melted POF spreads in this portion, so that the end face of the POF can be processed without causing chipping or flashing. That is, the tip of the POF has an enlarged portion 16 that is enlarged from the core diameter. The plug 107 is generally made of a metal such as stainless steel or aluminum because heat resistance is required. Further, a flat portion 13 is formed at the tip of the plug 107 in order to maintain strength.
[0014]
[Patent Document 1]
JP-A-11-27217
Japanese Patent Laid-Open No. 61-122614 FIG. 1 and FIG.
JISC-5970
JISC-6387
[0015]
[Problems to be solved by the invention]
However, the method disclosed in Japanese Patent Application Laid-Open No. 11-27217 can prevent interference due to reflection of transmission light at the end face of the POF, but prevents interference due to light reflected by the plug or the receptacle. I can't. As described above, the POF is fixed to the plug, and the plug is inserted into the receptacle. In the optical communication module using POF, the processing accuracy of each component is low in order to reduce the cost, and the transmission light is made incident on the outer peripheral portion of the POF in order to perform full-duplex communication by space separation. In some cases, a part of is not irradiated on the end face of the POF, but on the outer plug or receptacle. For example, in the plug shown in FIG. 8, the transmission light irradiated to the plug inclined portion 12 and the plug flat portion 13 is likely to be reflected or scattered toward the light receiving element side and easily cause interference.
[0016]
In addition, communication between electronic devices requires communication over a short distance of about 1 m and can be easily inserted and removed. Therefore, it is necessary to consider eye safety. The amount of light (the amount of light emitted from the optical fiber) must be set low. However, when a semiconductor laser is used as the light source of the optical communication module, the following problems occur when the light amount of the light source itself is reduced.
[0017]
As shown in FIG. 9, the relationship between the driving current of the semiconductor laser and the optical output can be approximated by the characteristics of a broken line formed by two straight lines in a region where the optical output is not saturated. Of these, the area A is a laser oscillation area, and the area B is a spontaneous emission area. When pulse input is performed with a current larger than the threshold current (Ith) as the bias current, the light output increases even at “0” of the pulse signal, and the extinction ratio increases. Conversely, if a current lower than Ith is taken as the bias current, the pulse width is reduced (duty ratio change) due to oscillation delay. Therefore, normally, the bias current is set in the vicinity of Ith. In this case, since spontaneous emission light is present even when the pulse signal is “0”, the extinction ratio is determined from the ratio of the spontaneous emission light and the light output when the pulse signal is “1”. For example, in the case of a semiconductor laser with spontaneous emission of 0.3 mW, the maximum output (output when the pulse signal is “1”) needs to be set to 3 mW or more in order to obtain an extinction ratio of 10 or more.
[0018]
That is, if the amount of transmitted light is reduced by reducing the output of the semiconductor laser, it will be difficult to satisfy the extinction ratio, and if the bias current is reduced, the duty ratio will change, causing a problem. For this reason, it is necessary to reduce the amount of transmitted light by reducing the coupling efficiency (transmission efficiency) between the light emitted from the semiconductor laser and the optical fiber. As a method of reducing the transmission efficiency, there is a method of reducing the amount of light using a filter or a polarizing element having a low light transmittance, but the number of parts increases and the cost increases. For this reason, a method of cutting a light beam having a large emission angle by the transmission lens by reducing the diameter of the transmission lens that collects the emitted light from the light emitting element and couples it to the optical fiber is common.
[0019]
However, this method has a problem in that light that does not actually contribute to transmission (light that is cut by the transmission lens) increases, and thus interference due to internal light tends to increase. In particular, in order to perform full-duplex communication using a single optical fiber, it is necessary to efficiently couple the received light emitted from the optical fiber to the light receiving element. However, when the reception efficiency is increased, light due to near-end reflection and internal disturbance light is also received efficiently, and there is a problem that interference increases. Further, the internal disturbance light is also reflected on the light receiving element 105 side by a plug or a receptacle, so that interference easily occurs.
[0020]
These interferences can be dealt with by improving the accuracy of the components, but in that case, the feature that the optical communication module using POF is inexpensive and easy to manufacture is lost.
[0021]
On the other hand, Japanese Patent Application Laid-Open No. 61-122614 discloses a method of reducing stray light by attaching a light blocking object to a collimator lens used in an optical isolator.
[0022]
That is, by inserting a light shield between the semiconductor laser and the collimator lens, stray light generated in the lens is reduced, stray light is prevented from returning to the semiconductor laser, and the semiconductor laser can be driven stably. ing.
[0023]
However, it prevents the light emitted from itself from returning to its original state, and does not prevent interference with the light receiving element, which is a problem in a full-duplex optical communication module using a single-core POF. Further, it is intended to reduce stray light in the lens, and cannot prevent stray light in the optical communication module or scattered light from an optical fiber plug or the like. Further, the light emitting point of the semiconductor laser is very small, and light returning to the light emitting point may be prevented. However, the optical communication module needs to be separated from the received light. For this reason, it is more difficult to reduce internal disturbance light. Furthermore, when inserting a light-shielding object, it is necessary to pay attention to management of the insertion accuracy, adhesion, deterioration due to changes over time, etc., which is expensive and problematic in terms of performance.
[0024]
The present invention has been made in view of these problems. Full duplex duplex communication is possible with a single plastic optical fiber, and in particular, crosstalk due to near-end reflection and internal disturbance light is simplified. An inexpensive and small-sized optical communication module that can be reduced is provided.
[0025]
[Means for Solving the Problems]
That is, the present invention is an optical communication module capable of transmitting and receiving an optical signal using a single plastic optical fiber, and receives a light emitting element that generates transmission light and received light emitted from the plastic optical fiber. A light receiving element, an optical component for condensing transmission light and / or reception light, and a receptacle having an opening for inserting a plug attached to an end of the plastic optical fiber, the plastic light The fiber has an enlarged portion whose diameter is larger than the core diameter at its end, and the enlarged portion around the tip of the plug and / or the plastic optical fiber when the plug is inserted into the receptacle To prevent interference from unnecessary light irradiating from the optical component side. Part of the receptacle The present invention relates to an optical communication module formed.
[0026]
The present invention further provides the following optical communication module.
The optical communication module according to the above, wherein the interference preventing unit is formed in a part of the receptacle.
[0027]
The optical communication module according to any one of the above, wherein the crosstalk prevention unit has a conical shape whose diameter gradually increases from the side on which the optical component is disposed toward the plastic optical fiber side.
[0028]
The optical communication unit according to any one of the above, wherein the crosstalk prevention unit has a shape inclined from an optical axis center on the plastic optical fiber side toward an outer peripheral direction with a side where the optical component is disposed as a tip. module.
[0029]
The optical communication module according to any one of the above, wherein the crosstalk prevention unit is arranged so as to shield light irradiated from the optical component side so as not to irradiate an end of the plug.
[0031]
The optical communication module according to any one of the above, wherein a part of the interference prevention unit and a part of the optical component are arranged in contact with each other.
[0032]
The optical communication module according to any one of the above, wherein the crosstalk prevention unit is formed only in the vicinity of the end face of the plastic optical fiber where the transmission light is incident.
[0033]
The optical communication module according to any one of the above, wherein a surface of the crosstalk prevention unit facing the plastic optical fiber is inclined with respect to an optical axis of the plastic optical fiber.
[0034]
With the above configuration, it is possible to perform full-duplex optical communication using a single optical fiber with reduced interference due to internal light such as near-end reflection and stray light.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a schematic diagram showing a configuration of an optical communication link. The optical communication link 3 is connected to an optical fiber 2 for bidirectional transmission of modulated light suitable for transmission based on a data signal to be transmitted, and to be optically coupled to both ends of the optical fiber 2. Each optical communication module 1 is provided.
[0036]
FIG. 2 is a schematic diagram showing the optical communication module according to the first embodiment of the present invention. The optical communication module 1 includes a light emitting element 4 that generates transmission light 8 that is modulated light based on a data signal, a light receiving element 5 that receives reception light 9 from the optical fiber 2 and generates a data signal, and light emission. A transmission lens 6 that condenses light emitted from the element 4 and couples it to the optical fiber 2, a rising mirror 15 that changes the direction of the transmission light 8 and couples it to the optical fiber 2, and the optical fiber 2 can be inserted and removed. It is comprised from the receptacle 10 which has an opening part. The tip of the optical fiber 2 is bonded and fixed to the plug 7, and the optical fiber 2 and the optical communication module 1 are optically coupled by being inserted into the opening of the receptacle 10 that is a part of the optical communication module 1.
The light generated by the light emitting element 4 diverges radially according to the radiation angle of the light emitting element 4. The divergent light is converted into an arbitrary numerical aperture by the transmission lens 6 and condensed. The collected light changes its direction by the rising mirror 15 and enters the optical fiber 2. The position of the optical fiber 2 on which the transmission light 8 is incident is the outer peripheral portion of the optical fiber 2. The transmission light 8 is condensed on a substantially circle having a diameter of about several hundreds μm at the end face of the optical fiber 2. In POF, since the core diameter is large, the condensing area may be relatively large, and even if the axial deviation is somewhat caused by increasing the condensing area, a part of the transmission light 8 is incident on the optical fiber 2. The light can be collected by an inexpensive optical system. Received light 9 emitted from the optical fiber 2 is emitted at an emission angle determined by the numerical aperture of the optical fiber 2 and is coupled to the opposing light receiving element 5. As described above, when the transmission light 8 and the reception light 9 are spatially separated within the aperture of the optical fiber 2, the reception light 9 emitted from the position where the transmission light 8 of the optical fiber 2 enters the light receiving element 5. Since coupling is not performed, and the position of the optical fiber 2 on which the transmission light 8 is incident is located on the outer peripheral portion of the optical fiber 2, the reception light 9 can be coupled to the light receiving element 5 more efficiently.
[0037]
A part of the transmission light 8 incident on the optical fiber 2 is reflected by the end face of the optical fiber 2 (reflected light 14). The reflected light 14 of the transmission light 8 from the optical fiber 2 is reflected in the outer peripheral direction of the optical fiber 2 because the end face of the optical fiber 2 is processed into a spherical surface, and is not coupled to the light receiving element 5 and reflected at the near end. Interference caused by can be prevented.
[0038]
Further, as described above, in the optical communication module 1 using POF as the transmission medium, the accuracy of the component parts is low due to the low price, and the transmission light 8 is used for full duplex communication by space separation. Since the light is incident on the outer peripheral portion of the fiber 2, a part of the transmission light 8 may be irradiated on the outer peripheral portion without being incident on the optical fiber 2 due to an axial deviation of the optical fiber 2 or the like. In the optical communication module 1, an interference prevention unit 11 is formed in a part of the receptacle 10. The interference preventing unit 11 is configured so that the enlarged light 16 formed during the end face processing of the optical fiber 2, the inclined part 12 of the plug 7, and the flat part 13 are not irradiated with the transmission light 8 or the internal disturbance light in the optical communication module 1. Has been placed.
[0039]
Since the interference preventing unit is configured so that a part of the plug is shielded from the optical component side, interference due to reflection / scattering from the plug can be reduced.
[0040]
The plastic optical fiber has an enlarged part whose diameter is larger than the core diameter at the end, but the crosstalk prevention part is arranged so that a part or all of the enlarged part is shielded from the optical component side. Further, interference due to reflection / scattering from the enlarged portion of the optical fiber and / or the inclined portion of the plug can be reduced.
[0041]
The inner wall portion of the receptacle 10 may be formed of a material having a high light absorption rate such as black. Since the plug 7 is generally made of metal, the reflectance can be significantly reduced by preventing the plug 7 from being irradiated with the transmission light 8, and interference due to near-end reflection can be reduced. Also, the assembly accuracy can be improved by forming the interference preventing part integrally with the receptacle.
[0042]
Further, the surface on the side where the optical component of the interference preventing unit 11 is arranged has a conical shape whose diameter increases in the direction from the distal end side of the optical fiber 2 to the optical fiber side. Since the crosstalk prevention part has a conical shape along the end face of the optical fiber, it is possible to reliably shield the enlarged part of the optical fiber and the optical fiber plug, and reliably reduce interference due to near-end reflection and internal disturbance light. can do. That is, the transmission light 8 that is originally applied to the inclined portion 12 and the flat portion 13 of the plug 7 is applied to the interference preventing portion 11 and is reflected in the outer peripheral direction of the optical fiber 2 by the conical shape (second reflected light 17). Therefore, interference due to near-end reflection can be prevented more reliably.
[0043]
Further, since the interference preventing unit has an inclined shape that spreads from the side where the optical components of the optical communication module are arranged toward the optical fiber side, the transmission light 8 kicked by the transmission lens 6 and the optical communication module 1 Internal disturbance light scattered inside can be prevented from being reflected by the inclined portion toward the light receiving element 5 and can be prevented from being coupled to the light receiving element. Therefore, the transmission lens 6 having a small diameter can be used, and it becomes easy to solve the problems of eye safety and extinction ratio.
[0044]
The optical fiber side surface of the interference preventing unit 11 may have a conical shape like the optical component side surface. However, by forming all or part of the side surface along the outer periphery of the end surface of the optical fiber 2, the optical fiber 2 It is possible to cope with any axis misalignment, it is possible to reliably shield the enlarged portion 16 and the plug 7 of the optical fiber 2, and to reliably reduce interference due to near-end reflection and internal disturbance light. .
[0045]
In addition, when a part of the light emitted from the optical fiber 2 is reflected by a part of the optical communication module 1 and coupled again to the optical fiber 2, the light propagates through the optical fiber 2 and is coupled to the other optical communication module. There is interference (interference due to reflection of the other module). In order to prevent interference due to the reflection of the counterpart module, the surface (reflection coupling prevention surface) facing the optical fiber 2 of the interference preventing unit 11 is inclined with respect to the optical axis of the optical fiber 2 (the reflected light is an opening of the optical fiber 2). It may be made larger than the number, specifically about 10 ° if the numerical aperture is about 0.3). The light applied to the reflection coupling prevention surface is reflected and returns to the optical fiber 2 side again, but the reflection angle is increased by the reflection coupling prevention surface 12, so that the reflection module is not coupled to the optical fiber 2 and the counterpart module. Interference due to reflection can be reduced.
[0046]
Furthermore, the interference preventing unit 11 also has a role as a stopper for positioning the plug 7 and the optical communication module 1. The insertion depth and position of the plug 7 are regulated by the interference preventing unit 11. Moreover, since each optical component is positioned with respect to the receptacle 10, both can be aligned via the receptacle 10. FIG.
[0047]
Next, each component of the optical communication module 1 shown in FIG. 2 will be described.
As the optical fiber 2, a large-diameter optical fiber 2 such as POF is used. POF has a core made of a plastic having excellent light transmission properties such as PMMA (Poly (methyl methacrylate) and polycarbonate, and a clad is made of a plastic having a refractive index lower than that of the above core. Since it is easy to increase the diameter of the core from about 200 μm to about 1 mm as compared with the quartz optical fiber, the coupling adjustment with the optical communication module 1 is easy, and an inexpensive optical communication link 3 can be obtained. As shown in this embodiment, when the transmission light 8 and the reception light 9 are spatially separated, it is preferable to use a core having a core diameter of about 1 mm.
[0048]
As the light emitting element 4, a semiconductor laser or a light emitting diode (LED) is used. The wavelength of the light emitting element 4 is preferably a wavelength with a small transmission loss of the optical fiber 2 to be used and is inexpensive. For example, when POF is used as the optical fiber 2, a semiconductor laser having a wavelength of 650 nm, which is mass-produced by a DVD or the like, can be used. Further, a monitoring photodiode is disposed at the rear of the light emitting element 4 so as to keep the light quantity of the light emitting element 4 constant.
[0049]
As the light receiving element 5, the intensity of the received modulated light is converted into an electric signal, and a photodiode having high sensitivity in the wavelength region of the light emitting element 4 is used. For example, a PIN photodiode or avalanche photodiode made of silicon is used. Etc. are used.
[0050]
The receptacle 10 is made of plastic and is manufactured by injection molding or the like. It is preferable that the hue has a high absorptance at the light wavelength used, such as black. By forming a positioning portion for aligning each optical component in the receptacle 10, the optical communication module 1 can be easily assembled.
[0051]
As described above, by using the optical communication module 1 shown in the first embodiment, it is possible to prevent near-end reflection and interference due to internal light due to stray light. Optical communication is possible. In particular, since it is possible to use a simple and inexpensive optical system, it is possible to obtain the optical communication module 1 that can be manufactured at low cost and easily. Here, the interference preventing portion is provided in a part of the receptacle, but a configuration in which a light absorbing member is directly formed on the end portion of the fiber to shield light is also possible.
[0052]
(Second embodiment)
Subsequently, a second embodiment will be described with reference to FIG. In the second embodiment, members having the same functions as those described in the first embodiment are assigned the same member numbers as in the first embodiment, and the description thereof is omitted. . In this embodiment, an optical communication module 1 having an optical system different from that of the first embodiment is shown.
[0053]
The transmission light 8 generated by the light emitting element 4 radiates radially according to the radiation angle of the light emitting element 4. Thereafter, the transmission light 8 is converted into an arbitrary numerical aperture by the transmission lens 6 and condensed, passes through the optical member 18, and is coupled to the optical fiber 2. The received light 9 emitted from the optical fiber 2 is reflected in the direction of the light receiving element 5 by the condenser mirror 19 and is condensed by the condenser mirror 19 having a curvature and coupled to the light receiving element 5. The optical member 18 has a prism 20 that is inclined with respect to the optical axis of the optical fiber 2 on the surface from which the transmission light 8 is emitted. The optical member 18 refracts the transmission light 8 and makes it incident on the optical fiber 2. A part of the condensing mirror 19 is arranged close to the optical fiber 2.
[0054]
A part of the transmission light 8 incident on the optical fiber 2 is reflected by the end face of the optical fiber 2. The reflected light of the transmission light 8 on the optical fiber 2 is shielded by the condensing mirror 19 and is not coupled to the light receiving element 5, and interference due to near-end reflection can be prevented. Also, interference due to internal light can be prevented because the transmission mirror and the reception block are separated by the condensing mirror 19. However, the light reflected and scattered by a part of the plug 7 and the receptacle 10 of the optical fiber 2 may be scattered in an unexpected direction, and it is difficult to completely separate the scattered light. In order to prevent the interference due to the scattered light, the interference prevention unit 11 is formed in a part of the receptacle 10.
[0055]
In the present embodiment, the interference prevention unit 11 is formed only in the vicinity (near) where the transmission light 8 is incident. The crosstalk prevention unit 11 is arranged so that the enlarged portion 16 formed during the end face processing of the optical fiber 2, the inclined portion 12 of the plug 7, and the flat portion 13 are not irradiated with the transmission light 8 or the internal disturbance light in the optical communication module 1. The shape is an inclined shape that spreads from the side where the optical component is disposed toward the optical fiber 2 side. Since the transmission unit and the reception unit are separated by the condensing mirror 19, it is not necessary to form the interference prevention unit 11 on the reception unit side (the lower side in FIG. 3). Further, since the transmission / reception is separated in the vertical direction of FIG. 3 by the condensing mirror 19, the crosstalk prevention unit 11 prevents the transmission light 8 from being reflected and scattered on the receiving unit side (lower side of FIG. 3). The shape is a shape having an inclination in an inclined shape that spreads from the side where the optical component is disposed toward the optical fiber 2 side.
[0056]
The optical member 18 (the mirror can be formed by vapor-depositing a metal) is made of plastic such as PMMA or polycarbonate, and is manufactured by injection molding or the like. A metal thin film having high reflectivity such as aluminum or gold is formed on the side to be a reflection mirror (also a condensing mirror) by vapor deposition or the like. The optical member 18 condenses the transmission light 8 and couples it to the optical fiber 2, the prism 20 that refracts the transmission light 8 and makes it incident on the optical fiber 2, and a light emitting element (not shown). 5 and an uneven portion for positioning used for alignment with the light receiving element 4 is formed. Since one optical member 18 is provided with a number of functions in this way, the number of constituent members can be greatly reduced, and tolerances during assembly can be reduced, so that a small optical communication module 1 can be obtained at low cost. It becomes possible.
[0057]
A part of the optical member 18 is disposed in contact with or close to a part of the interference preventing unit 11. If there is a gap between the optical member 18 and the interference prevention unit 11, interference due to internal disturbance light is likely to occur due to the reflected light between them. Further, the prism 20 refracts the transmission light 8 and makes the transmission light 8 tilted from the outer peripheral portion of the optical fiber 2 toward the inner peripheral portion. This makes it difficult for the transmission light 8 to be applied to the inclined portion 12 of the plug 7. Further, the interference preventing unit 11 is not formed on the receiving unit side. A part of the light emitted from the optical fiber 2 is also emitted from the enlarged portion 16 of the optical fiber 2. For this reason, it is possible to improve the reception efficiency by not forming the interference prevention unit 11 on the receiving unit side.
[0058]
In addition, when a part of the light emitted from the optical fiber 2 is reflected by a part of the optical communication module 1 and coupled again to the optical fiber 2, the light propagates through the optical fiber 2 and is coupled to the other optical communication module. There is interference (interference due to reflection of the other module). In order to prevent the interference due to the reflection of the counterpart module, the surface (reflection coupling prevention surface 21) of the interference prevention unit 11 that faces the optical fiber 2 is inclined with respect to the optical axis of the optical fiber 2 (the reflected light is the optical fiber 2). It is set to be larger than the numerical aperture, specifically about 10 ° if the numerical aperture is about 0.3). The light applied to the reflection coupling prevention surface 21 is reflected and returns to the optical fiber 2 side again. However, the reflection angle is increased by the reflection coupling prevention surface 12, so that it is not coupled to the optical fiber 2. That is, the reflected light is converted to an angle larger than the numerical aperture of the optical fiber 2 by the reflection coupling prevention surface 21. The prism 20 also has the same function, and reduces interference due to reflection of the counterpart module.
[0059]
This embodiment is merely an example, and the present invention is characterized in that the interference prevention unit 11 is formed in a part of the receptacle 10 and, of course, can be applied to other optical arrangements.
[0060]
【The invention's effect】
According to the present invention, it is possible to provide a full duplex duplex communication module using a single plastic optical fiber with reduced crosstalk due to near-end reflection and internal light at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating the configuration of an optical communication link according to the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of an optical communication module according to a first embodiment of the present invention.
FIG. 3 is a schematic diagram illustrating the configuration of an optical communication module according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram illustrating a configuration of an optical communication module using a glass optical fiber.
FIG. 5 is a schematic diagram illustrating a configuration of an optical communication module using a conventional plastic optical fiber.
FIG. 6 is a schematic configuration diagram illustrating a conventional optical communication module capable of full-duplex communication.
FIG. 7 is a diagram for explaining a relationship between a transmission light coupling position on an end face of an optical fiber and a reception area;
FIG. 8 is a view for explaining a conventional plug shape for a plastic optical fiber.
FIG. 9 is a graph illustrating the relationship between the current of a semiconductor laser and the optical output.
[Explanation of symbols]
1: Optical communication module
2: Optical fiber
3: Optical communication link
4: Light emitting element
5: Receiving element
6: Transmitting lens
7: Plug
8: Transmitted light
9: Received light
10: Receptacle
11: Interference Prevention Department
12: Plug inclined part
13: Plug flat part
14: Reflected light (near-end reflected light)
15: Start-up mirror
16: Enlarged part
17: Second reflected light
18: Optical member
19: Condensing mirror
20: Prism
21: Antireflection coupling surface
101: Optical communication module
102: Optical fiber
104: Light emitting element
105: Light receiving element
106: Transmission lens
108: Transmitted light
109: Received light
110: Receptacle
114: Reflected light (near-end reflection)
115: Start-up mirror
121: Ferrule

Claims (7)

An optical communication module capable of transmitting and receiving an optical signal using a single plastic optical fiber, a light emitting element for generating transmission light, a light receiving element for receiving reception light emitted from the plastic optical fiber, and transmission An optical component for collecting light and / or received light, and a receptacle having an opening for inserting a plug attached to an end of the plastic optical fiber, the plastic optical fiber at the end An enlarged portion whose diameter is larger than the core diameter, and when the plug is inserted into the receptacle, a part of the enlarged portion around the distal end portion of the plug and / or the plastic optical fiber, so as to shield the unnecessary light is irradiated from the optical component side, and characterized in that the interference preventing portion is formed in a portion of the receptacle That optical communication module. Optical communication module 請 Motomeko 1 wherein you wherein interference preventing portion has a conical shape that the diameter thereof becomes gradually wider toward the plastic optical fiber side from the side where the optical component is arranged. The interference preventing portion includes a tip side, wherein the optical component is disposed, on any one of claims 1 to 2, characterized in that an inclined shape toward the outer circumferential direction from the center of the optical axis of the plastic optical fiber end The optical communication module described. Optical communication module according to any of claims 1 to 3 wherein the interference preventing portion is characterized by being arranged to shield the unnecessary light is irradiated from the optical component side so as not to be irradiated to an end of the plug. Optical communication module according to any one of claims 1 to 4, characterized in that placed in contact with a portion of the optical component part of the interference preventing portion. Optical communication module according to any of claims 1 to 5 wherein the interference preventing portion is characterized in that the transmission light of the plastic optical fiber end surface is formed only in the vicinity of the incident. The optical communication module according to any one of claims 1 to 6 , wherein a surface of the interference preventing unit facing the plastic optical fiber is inclined with respect to an optical axis of the plastic optical fiber.

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